Genetic recombination is a process in which information from one DNA molecule is transferred to a second DNA molecule. In E. coli it is essential for the repair of damaged DNA and the maintenance of cell viability. E. coli provides an excellent system for the analysis of the enzymatic events involved in genetic recombination because of its well defined genetics and ease of handling. As a starting point for this work, exonuclease VIII, an enzyme involved in one type of indirect suppression of recB and recC deficiency, will be purified and characterized. In addition, exonuclease I will be studied in more detail to determine its role in the indirect suppression of recB and recC mutations. Attempts will be made to amplify the amounts of exonuclease I by construction of a hybrid colicin which carries the sbcB gene. Employing a new assay for genetic recombination, mutants will be analyzed for both increased and decreased levels of recombination. Finally, new conditional recB and recC mutants will be isolated employing the procedure of localized mutagenesis. BIBLIOGRAPHIC REFERENCES: Zieg, J. and S.R. Kushner, (1975) A New Assay for Genetic Recombination in E. coli. Abstracts of the Annual Meeting of the ASM, p. 98; Champney, W.S., S.R. Kushner and V. Maples. (1975) Isolation of Temperature-Sensitive Mutants in Ribosomal Proteins. Abstracts of the Annual Meeting of the ASM, p. 116.